This invention relates to a fuel pump drive apparatus for a fuel injection equipment for an internal combustion engine, and more particularly to a fuel pump drive apparatus for driving a fuel pump of a fuel injection equipment for an internal combustion engine.
A fuel injection equipment for an internal combustion engine generally includes a fuel pump, a fuel injector or fuel injection valve fed with fuel by the fuel pump, a pressure regulator for controlling a pressure of fuel fed from the fuel pump to the fuel injector, an injector drive circuit for feeding a drive current to the injector in response to an injection command pulse, a fuel injection control unit for feeding the injector drive circuit with an injection command pulse so as to render the amount of fuel injected from the injector equal to a fuel injection quantity demanded by the internal combustion engine at each of rotational speeds of the engine.
The fuel pump is constituted by a drive source such as a pump drive motor or the like which is fed with a drive current from a DC power supply, as well as a pump mechanism driven by the drive source. The fuel pump functions to pump oil out of a fuel tank to feed it to the injector.
The fuel injector includes a valve body provided at a distal end thereof with an injection port, a valve arranged in the valve body to selectively close the injection port and a solenoid coil for actuating the valve and functions to feed fuel from the fuel pump into the valve body. The injector is arranged so as to inject fuel into a fuel injection space such as an interior of an air intake pipe of the internal combustion engine, an interior of a cylinder thereof or the like.
The injector drive circuit is constituted by a switch circuit including a transistor or the like arranged so as to act as a switching element. Feeding of an injection command pulse to the injector drive circuit permits the switching element of the injector drive circuit to be turned on, so that a drive current may be fed to the solenoid coil. This results in the valve of the injector being open, so that fuel fed from the fuel pump is injected into the fuel injection space of the engine through the injection port of the injector. The amount of fuel injected from the injector or a fuel injection quantity is determined depending on an injection period or a period of time during which the injection port is kept open and a pressure difference between a pressure of fuel fed from the fuel pump to the injector and a pressure in the fuel injection space or an atmospheric pressure. The pressure difference is referred to also as "fuel pressure" herein.
A time lag of a predetermined length exists between feeding of an injection command pulse to the drive circuit and actual opening of the valve of the injector. Likewise, a time lag exists between feeding of the injection command signal to the drive circuit and closing of the valve. This fails to permit a pulse width of the injection command pulse and an actual injection period or effective injection period to be equal to each other. A length of the effective injection period is determined depending on a pulse width of the injection command pulse. Thus, control of the pulse width of the injection command pulse permits the effective injection period to be controlled.
As noted from the above, the amount of fuel injected from the injector or a fuel injection quantity therefrom is determined depending on the fuel pressure and effective injection period. A variation in both fuel pressure and effective injection period causes the control to be complicated and/or troublesome. Thus, actually the fuel pressure is controlled so as to be substantially constant by the pressure regulator, resulting in the fuel injection quantity being determined essentially or directly depending on a pulse width of the injection command signal. Also, the pulse width of the injection command pulse is varied depending on various control conditions such as a degree of opening of a throttle valve, a rotational speed of the engine, an atmospheric pressure, a temperature of air sucked, a temperature of cooling water for the engine and the like, to thereby control the fuel injection quantity.
The pressure regulator functions to return fuel surplus in a passage defined between the fuel pump and an inlet of the injector toward the fuel tank to permit a fuel pressure at the inlet of the injector to be kept at a constant level when the fuel pressure exceeds a predetermined adjustment value.
The pressure regulator of this type tends to cause the adjustment value to be affected by a flow rate of the surplus fuel returned toward the fuel tank or a return flow rate of the surplus fuel. For example, the pressure regulator tends to cause the adjustment value to be substantially varied due to an excessive decrease or increase in return flow rate of the surplus fuel, to thereby be deteriorated in controllability thereof. Thus, in order to keep the fuel pressure substantially constant by means of the pressure regulator of this type, it is required that a return flow rate of the surplus fuel returned toward the fuel tank through the pressure regulator is kept within a suitable range or a range sufficient to ensure appropriate controllability of the pressure regulator.
As described above, in the fuel injection equipment, it is required to keep the fuel pressure at a predetermined level in order to permit the fuel injection quantity to be controlled depending on a pulse width of the injection command pulse. For this purpose, it is generally required that the amount of fuel to be fed to the injector is always increased as compared with the amount of fuel demanded by the internal combustion engine or a fuel demand of the engine and driving of the fuel pump is carried out so as to ensure that the amount of surplus fuel is kept within an appropriate range.
The conventional fuel pump drive apparatus which has been used for the internal combustion engine fed with fuel by means of the fuel injection equipment includes a magneto driven by the internal combustion engine and a battery charged through a battery charging circuit by means of a voltage induced across a battery charging coil arranged in the magneto and is constructed so as to continuously apply a voltage across the battery to the fuel pump during operation of the engine, to thereby drive the fuel pump. The voltage across the battery is applied to other loads as well as to the fuel pump.
The battery charging circuit is constituted by a rectification circuit for rectifying an AC voltage across the battery charging coil and a voltage regulator which functions to restrict a voltage applied to the battery to a predetermined level or below.
The voltage across the battery charged by an output of the magneto is not constant and is varied depending on a state of charging of the battery, a state of loads, a capability of a battery charging generator and the like. Thus, driving of the fuel pump by means of the voltage across the battery as in the conventional fuel pump drive apparatus causes the amount of fuel discharged from the fuel pump to be affected by a variation in voltage cross the battery, resulting in being varied. In particular, in the case that a load other than the fuel pump connected to the battery is a large-current load such as a tilt motor for an outboard motor, a horn, a head light, a motor for starting the internal combustion engine or the like, a voltage across the battery is substantially reduced, to thereby highly decrease the amount of fuel discharged from the fuel pump when the load is connected to the battery.
Thus, in the prior art, the fuel pump is designed or constructed so as to discharge fuel in an mount equal to or more than an expected maximum fuel demand of the internal combustion engine, when the voltage across the battery is reduced to a minimum level. Unfortunately, such construction causes the amount of fuel discharged from the fuel pump to be excessive, leading to an excessive increase in amount of fuel returned through the pressure regulator, resulting in controllability of the pressure regulator being deteriorated, when any load other than the fuel pump is separated from the battery to increase the voltage across the battery.
Such deterioration in control of a fuel pressure by the pressure regulator fails to permit the fuel injection quantity or the amount of injection of fuel to be determined essentially depending on a pulse width of the injection command pulse, leading to a failure in appropriate control of the amount of injection of fuel, so that the prior art substantially fail to derive desired performance of the internal combustion engine.
Also, when the fuel pump is driven by the battery, the fuel pump is required to exhibit excessive performance, leading to an excessive increase in power consumption of the fuel pump.